UC San Diego

The brain bidirectionally communicates with the gut to control food intake and energy balance, which becomes dysregulated in obesity. For example, endocannabinoid (eCB) signaling in the small-intestinal epithelium (SI) is upregulated in diet-induced obese mice (DIO) and promotes overeating by a mechanism that includes inhibiting gut-brain satiation signaling. Upstream neural and molecular mechanism(s) involved in overproduction of orexigenic gut eCBs in DIO, however, are unknown. We tested the hypothesis that overactive parasympathetic signaling at muscarinic acetylcholine receptors (mAChRs) in the SI increases biosynthesis of the eCB, 2-arachidonoyl-sn-glycerol (2-AG), which drives hyperphagi-a via local CB₁Rs in DIO. Male mice were maintained on a high-fat/high-sucrose western-style diet for 60 days, then administered several mAChR antagonists 30 min prior tissue harvest or a food intake test. Levels of 2-AG and activity of its metabolic enzymes in the SI were quantitated. DIO mice, when compared to those fed a low-fat/no-sucrose diet, displayed increased expression of cFos protein in the dorsal motor nucleus of the vagus, which suggests increased activity of efferent cholinergic neurotransmission. These mice exhibited elevated levels of 2-AG biosynthesis in the SI, which was reduced to control levels by mAChR antagonists. Moreover, the peripherally-restricted mAChR antagonist, methylhomatropine bromide, and the peripherally-restricted CB₁R antagonist, AM6545, reduced food intake in DIO mice for up to 24 h but had no effect in mice conditionally deficient in SI CB₁Rs. These results suggest that hyperactivity at mAChRs in the periphery increases formation of 2-AG in the SI and activates local CB₁Rs, which drives hyperphagia in DIO.Significance Statement Gut-brain signaling controls food intake and energy homeostasis; however, it is poorly understood how gut-brain signaling becomes dysregulated in obesity. In this study, we demonstrated that brain to gut communication is altered in obesity, leading to an increase in endocannabinoid signaling in the GI tract, which drives overeating. Acutely blocking activity at muscarinic acetylcholine receptors in the periphery attenuates intestinal endocannabinoid production and calorie intake in obese animals. This effect was absent in mice conditionally lacking CB₁Rs in the intestinal epithelium. These findings expand our understanding of the complex pathophysiology associated with obesity and mechanisms of brain-gut-brain signaling.